A pressure-sensitive adhesive (PSA) construction generally comprises a facestock and at least one layer of pressure-sensitive adhesive on the facestock, as well as a release surface. If they are to be used together, the pressure-sensitive adhesive and the facestock must not excessively adversely affect one another. The existence of adverse chemical or physical reactions between the facestock and the adhesive layer reduces the stability of the construction, and may effectively prevent an otherwise desired combination of materials.
For example, rubber-based adhesive compositions are known to form good adhesive layers, which can adhere to a wide variety of substrates. However, polyolefinic materials--often used in film facestock--are generally not suitable with a wide range of rubber-based pressure-sensitive adhesives, because of swelling which occurs over time when the two are adjacent to one another. This swelling manifests itself as wrinkling of the adhesive construction and/or a loss of adhesion. To avoid the problems associated with swelling, manufacturers, especially those who use polyolefinic facestocks, are often forced to use acrylic-based adhesives.
It has been found that the swelling is caused by the migration of mobile ingredients from the rubber-based adhesive layer to the facestock. The mobile ingredients include organic molecules, such as oils, liquid resins, and tackifiers, which are often added to the rubber-based polymer during manufacture to impart desired adhesive or other properties to the composition. Certain of these relatively mobile ingredients have an affinity for polyolefinic facestock material and, if so, may migrate to the facestock. The resulting swelling of the facestock, ingredients into the facestock, leads to wrinkling of the adhesive construction and/or loss of adhesion.
Under certain circumstances, migration may also occur between mobile species contained in a facestock and an underlying adhesive layer. For example, many polyvinylchloride (PVC) facestocks contain liquid plasticizers. These mobile ingredients may migrate, over time, into an adjacent layer of adhesive. Migration of mobile ingredients from a facestock into an adhesive layer may also lead to a loss of pliability or contraction of the facestock, and a concurrent loss of adhesion, as discussed in U.S. Pat. No. 3,547,852 issued to Burke.
Thus, it is desirable to develop pressure-sensitive adhesive constructions which minimize or prevent migration of species between facestock and underlying adhesive layers, so that facestocks may be used with a wider variety of adhesive formulations, and retain a useful product stability.